Excitons are bound electron-hole pairs that represent one kind of elementary electronic excitations in materials with screened Coulomb interactions. Excitons, in similarity to plasmons (collective oscillations of free electrons) and phonons (collective lattice vibrations), can strongly couple with electromagnetic waves in the form of polaritons. At optical frequencies, the interaction between matter and electromagnetic waves is encoded into the relative permittivity (ε). Extensive studies on surface plasmon- and phonon-polaritons relied on ε values that are near or below zero, which is essential for the confinement of light at sub-wavelength scales, and enabled numerous applications ranging from solar energy harvesting to ultrasensitive biosensing. Such regimes of ε arising from excitons, however, have been much less explored, due to 1) a limited number of materials exhibiting strong excitonic effects and 2) the difficulty of extracting the values of ε due to a lack of large-size materials typically needed for ellipsometry measurements. The recently re-emerged 2DHPs show extreme and tunable quantum-confinement effects and share the same layered structure as both artificially grown metal-dielectric superlattices and van der Waals materials such as h-BN. Development of a technique for characterizing the anisotropic permittivity, or, equivalently, the refractive index of 2DHPs and other small-sized materials is urgently needed. Understanding the similarity between excitons and other fundamental excitations, and their effect on ε is crucial for improved nanophotonic and optoelectronic applications utilizing 2DHPs and other quantum-well-like materials.